In recent years, particularly in advanced nations, the number of people suffered from neurological and psychiatric disorders has increased. Causes of these disorders are thought to be rapidly aging society and/or various stresses. More specifically, it is estimated that the number of people with dementia such as Alzheimer's disease has increased due to an age-associated decline in cerebral functions combined with some other factors. Furthermore, it is thought that the number of people with schizophrenia or depression has increased due to various stresses that exist in modern society.
Hitherto, it has been considered that cerebral nerve cells largely contribute to cerebral functions. For example, in the above described neurological disorders, although their respective causes are different, various changes including sclerosis, atrophy, death, or reduction of cerebral nerve cells can be observed therein. Therefore, there are expectations for a possible treatment to prevent progression of neurological disorders by hindering such changes in the cerebral nerve cells. For example, Patent Literature 1 discloses that dictyosterol has an effect of enabling survival and sustention of nerve cells when they are damaged and enhancing formation and outgrowth of neurites; and thereby suggests that dictyosterol may be used for treating neurological disorders. Furthermore, Patent Literature 2 suggests that a plasmalogen (phosphatidylethanolamine) has a nerve cell death inhibiting effect.
In addition, there is an expectation that a better therapeutic effect can be obtained by inducing neogenesis of cerebral nerve cells rather than stopping changes in cerebral nerve cells as described above. In recent years, it has been revealed that neogenesis of nerve cells are occurring even in adults of many mammals including humans. In particular, neogenesis of nerve cells in the hippocampal dentate gyrus is thought to have a large contribution in the development of regenerative therapy for neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. For example, it is reported that fluoxetine which is a therapeutic agent for depression increases the number of cerebral nerve cells in 3 to 4 weeks (Non-Patent Literature 1), and the increase is inferred to contribute to an antidepressive effect of the therapeutic agent.
However, substances having an effect of inducing neogenesis in cerebral nerve cells are almost unknown, and thereby there has been a desire for a new substance capable of inducing neogenesis in cerebral nerve cells safely and efficiently.